Redox systems obeying Marcus–Hush–Chidsey electrode kinetics do not obey the Randles–Ševčík equation for linear sweep voltammetry

The cyclic voltammetry of the reaction of a solution-phase species at a macroelectrode under semi-infinite diffusion is simulated assuming irreversible electrode kinetics within the Marcus–Hush–Chidsey model. The resulting peak currents are shown to deviate from the square root dependence on voltage scan rate predicted by the Randles–Ševčík equation. Simulated voltammetry of a surface-bound redox couple also shows deviations from the expected linear dependence of peak current on scan rate. These numerical findings are supported by analytical arguments and they provide simple method for a critical analysis of the kinetic model. In particular the sheer extent of published experimental work containing linear Randles–Ševčík plots suggests the need for significant refinement of the Marcus–Hush–Chidsey model before it is suitable for the analysis of experimental voltammetry.

► Marcus–Hush–Chidsey kinetics show deviations from the Randles–Ševčík equation.
► Deviations also seen in peak current-scan rate dependence for surface-bound species.
► Greatest differences seen for small reorganisation energy and low rate constants.
► Experimental conditions identified for observation of deviations.